DESCRIPTION: Elucidation of the regulatory steps in corneal collagen fibrillogenesis and matrix assembly will provide the foundation for understanding normal corneal development, growth, maturation and repair. In addition, definition of the regulatory steps is critical for understanding the development and maintenance of transparency, regulation of hydration as well as corneal pathobiologies such as edema, wound healing and some dystrophies. Our overall hypothesis is that corneal matrix assembly is a multi-step process with specific regulatory interactions at each step. This application addresses: (1) fibril nucleation at the keratocyte surface and its regulation by collagen I/V interactions;(2) fibril growth steps and their regulation by small leucine-rich proteoglycans;and (3) matrix integration/organization during development, growth and maturation involving fibril-associated collagens. The specific aims of this application are to: (aim 1) determine the role(s) of type V collagen in regulation of fibril nucleation, the specific domains responsible for regulation and the sites of action;(aim 2) determine the regulatory roles of decorin/biglycan and lumican/keratocan in regulation of fibril growth and packing necessary for corneal transparency;and (aim 3) determine the role(s) of the fibril-associated collagens, types XII and XIV in mediating the integration/maturation of the developing stroma. The hypotheses to be tested are: (aim 1) type V collagen is the key regulator involved in the nucleation of corneal fibril assembly;(aim 2) small leucine-rich proteoglycans regulate fibril growth steps and organization involving a coordinate regulation by 2 separate classes: Class I, decorin and biglycan and class II, lumican and keratocan;and (aim 3) fibril packing, stromal compaction and integration of the developing matrix are mediated by fibril-associated collagen types XII and XIV through their association with fibrils and ability to interact with other matrix molecules. Mouse models deficient in specific matrix molecules will be utilized and stromal development will be analyzed using biochemical, immunochemical, molecular and ultrastructural approaches. Binding assays and in vitro fibrillogenesis studies will be done in parallel to define specific functional interactions. Definition of the regulatory steps in corneal-specific matrix assembly provides the foundation to further our understanding of corneal repair/regeneration, pathobiologies and the modulation of these processes.